Quick acting make-and-break microswitch



March 14, 1967 S. D. MKlE 3,309,476

QUICK AcTNG MAKE-AND-BREAK MIcRoswITcH Filed Feb. 14, 1964 4 Sheets-Sheet 1 By y WMQ/

March 14, 1967 s. D. MCKlE QUICK ACTING MAKE-AND-BREAK MICROSWITCH 4 Sheets-Sheet 2 Filed Feb. 14, 1964 @www March 14, 1967 s. D. MGKIE 3,309,476

QUICK ACTING MAKE-AND-BEAK MICROSWITCH Filed Feb. 14, 1964 4 Sheets-Sheet 5 /4/foMM/vf March 14, 1967 s. D. MCKIE QUICK ACTING MAKE-AND-BREAK MIcRoswITcH 4 Sheets-Sheet 4 Filed Feb. 14, 1964 n D v www United States Patent() 3,3ii9,476 QUICK ACTING MAKE-AND-BREAK MICRGSWITCH Stephen Domville McKie, 317 Pennant Hills Road,

Thornleigh, New South Wales, Australia Filed Feb. 14, 1964, Ser. No. 344,991

Claims priority, application Australia, Feb. 25, 1963,

27,747/63; Aug. S, 1963, 34,018/63 4 Claims. (Cl. 200--67) This invention relates to a quick make-and-break microswitch. i n

Several types of microswitches are known. One known type of microswitch has the disadvantages that it must be manufactured very carefully to critical tolerances, it has a multipli-city of parts, and the moving or stressed member must be tensioned accurately. In another type of microswitch some of these disadvantages are overcome but the stressed member must' be tensioned accurately between two supporting rivets,frequiring a solid plate to act as a support for the stressed member, and again the tolerances are critical.

VThe -present invention provides a microswitch which overcomes these disadvantages. Apart from the fixed contacts only one moving member is required, and this may be secured directly to a plastic. base. Tolerances are not critical and the stressed member is blanked in such a way that it has built-in stress. Only one securing point for the stressed member is required. By small variations in design the -switch can be made to operate for displacements of an operating knob ranging from 3/10,000 inch to several thou-sandths of an inch, depending upon requirements.

It is an object of this invention to provide a quick makeand-break microswitch which has a single stressed contactcarrying metal member secured to a base at one point only, a Contact being provided remote from said one point, an aperture in the member extending from near the contact toward the `said one point, the member being st-ressed by permanently displacing metal at somepoint around the aperture whereby the member takes up a bowed formation, with means for applying pressure to the Vstressed Lmember betweenthe said one point and the nearest point on theaperture sofas to cause the centre of stress to pass from one side of the member to the other. One preferred shape of the aperture is triangular with the base near the contact and the apex pointing toward the ysaid one point; However the aperture may ybe circular, the member then being annular in shape. A transverse slot may be provided between the said one point and the point or points at which the member is supported from the base. The said support-points are preferably at the outside edges of the member. The concavity in the base under the member below the :pres-sure point may be small so that the member cannot be caused to take a permanent set upon a mechanical overload being placed on it. The stressed member may lbe pressed from bimetal strip to provide a temperature responsive switch.

Reference will now be made to the accompanying drawings in which: y

FIGURE 1 shows a microswitch in accordance with this invention in exploded form,

FIGURE 2 is a section along the length of an assembled microswitch according to FIGURE l,

FIGURE 3 is a sketch showing the stressed member in its normal state, Y

FIGURE 4 is a sketch showing that the application of pressure causes the stressed member to tlip over to open the switch contacts,

FIGURE 5 is an exploded view of a three pole microswitoh in accordance with this invention using approximately circularly apex-tuned stressed members,

- 3,309,476 vPatented Mar. 14, 1967 FIGURE 6 is an assembled view of the switch of FIG- URE 5 but without the cover,

FIGURES 7 and 8 are sketches of one of the stressed members of the switch of FIGURES 5 and 6 illustrating the operation of the switch,

FIGURE 9 is an exploded view of a flasher switch employing a microswitch in accordance withthis invention,

, FIGURE l0 is a longitudinal section of the switch of FIGURE 9,

FiGURE l1 is an exploded view of a switch known as an infinitely variable switch, and

FIGURE 12 is a section of the assembled switch of FiGURE 1l.

Referring now to FIGURES 1 to 4, which show a singlepole-double-throw switch, a rectangular plastic moulded base 1 is provided on the which the contacts are carried. The top surface of the base has a pillar 2 at one end of small area at the top to which the moving contact member, the stressed member 3, is secured as by riveting at 4. Adjacent the pillar but separated from it by a transverse slot 6 is a narrow transverse support 7 which is concave viewed from above, the concavity being of large radius, and having lips 8 at each end. Spaced from the support is a truncated triangular pillar 9 extending longitudinally of the base with its narrow end pointing toward the rst mentioned pillar 2. A rst xed contact strip 10 is secured in a longitudinal groove 11 in the top of the triangular pillar with one end, to which the contact 12 itself is secured, projecting over the base of the pillar. The second fixed contact 13 is immediately beneath and spaced from the first xed contact, lbeing secured through the base 1 as by riveting.

The Kmoving contact member 3 is basically a rectangular strip ot spring metal. At one end is an opening 14 by which the member is secured to the trst-mentioned-pillar. In front ot this opening is a transverse slot 15 which, when the member is secured to the base, cornes over the slot 6 in the base between the first-mentioned pilla-r 2 and the support 7. In front ot this again is an is-osceles triangular shaped aperture 16 of which the two equal sides are several times the length of the base. The apex of the triangle is near the transverse slot 15 in the moving contact member, and the base 17 is parallel to the narrow side of the strip and adjacent to the end of it farthest from the first-mentioned opening 14. During or after the blanking the metal i8 between the base of the triangular aperture and the end of the strip is displaced out of the plane of the strip, which has the eiect of pulling the two legs formed by the metal outside the l-ong sides of the triangle toward each other slightly. This in turn stresses the moving contact member so that it bows slightly along its length and very slightly across its width. The actual contact tips 19, 2d are secured on each side of the displaced base portion 18.

The pre-stressed lmoving contact member 3 is assembled to the base with the moving contact tips 19, 20 between the fixed contacts 12, 13, as is best seen in FIGURE 2 the triangular aperture 16 sur-rounding the triangular pillar 9, the opening i4 in one end over the screw or rivet 4 to which the member 3 is then secured, with the edges 21, 22 of the member immediately in front of the transverse slot 6 resting on the upper extreme edges of the concave support 7 on the base 1. The support 7 may be at the end of the aperture 16, or between it and the slot 15. The member is assembled with the bow upwardly directed so that the stressed member 3 is biased downwardly with the lower contact 20 in contact with the lower xed contact 13.

A cover 23 of insulating material is provided for the switch and carries a plunger 24 having one end extending through an opening 25 in the top of the cover and a its other end, of insulating material 26, resting on the movable contact member 3 at some point midway across its width. One preferred position of the plunger is the edge of the transverse slot nearest the moving contact: at this point the plunger travel is least to cause the switch to change over to make contact with the upper fixed conv tact but the pressure required is greatest. By moving along the strip toward the moving contact, for example to the position shown in FIGURE 2, the plunger travel increases but the pressure required decreases, until finally the switch will not operate. Pressure on the plunger, illustrated diagrammatically in FIGURE 4 by the arrow, displaces the bow downwardly until the centre of the members stress is above the strip, which then flips over and the moving contact rises to the position shown in FIGURE 4. The cover is secured to the base by a screw 27 which passes through the aperture 16 and is screwed into an opening 28 in the base.

To prevent the movable contact member 3 from rotation about its point of securement the base is provided with the small wings or lips 8 projecting above the member on each side adjacent to the concave support position 7. Means 29, 30, 31 for securing wires to the fixed and moving contacts are provided.

The main function ofthe slot 15 is to isolate to some extent the main part of the stressed member from the base to which it is rivetted. If the end of the stressed member is rivetted rigidly to the base more force is required to operate it. The larger the slot 15 the easier the switch is to operate but the lower the contact pressure. If a large slot is used then some pressure can be provided on the contact by stops, screws, et cetra.

If the 'plunger movement is to be minimised then, in addition to positioning the plunger 24 near the transverse slot 15, the support 7 beneath the moving contact member may be made at over all except a small area immediately beneath the plunger.

FIGURES 5 to 8 illustrate the use of stressed movable contact members which are substantially in the form of annular rings. With this form a number of stressed contact members can be piled above each other to give a multi-pole switch, and a three-pole switch is illustrated in these figures. Each movable contact member is an annular ring 40, 41, 42 having diametrically opposed outwardly extending lugs 43, 44, 4S and 46, 47, 48, and an internal arcuate projection 49, 50, 51 opposite the respective lugs 43, 44, V45. Slots such as 52 are provided behind each projection 49, 50, 51. The portions of the annular rings immediately behind the lugs 46, 47,748, and the lugs themselves in the case illustrated, are displaced downwardly to form grooves. As in the embodiment of FIGURES 1 to 4 this causes each stressed member to bow downwardly along the diameter containing the lugs e.g. lugs 43 and 46, and slightly across the diameter which is at right angles to that containing the lugs, as is illustrated in FIGURE 8.

Each stressed member is supported about, on or near its internal circumference, if the aperture had been a complete circle, by means of a forked member such as S3 having fingers 54 whose ends abut against the underside of the projection 49 (or 50 or 51 as the case may be). The end 56 of the forked member 53 is secured, along with'the lug 43 of the stressed member 41, in a slot 57 in the base moulding 58 by a rivet 55. The base moulding is castellated to provide additional slots S9, 60 for the ends of the forked members 53 53", so that when assembled as shown in FIGURE 6 the stressed members 40, 41, 42 are stacked at different levels above one another with the lugs displaced angularly with respect to each other. The base 58 is castellated similarly at diametrically opposite points to provide pillars 61, 62 which divide the lugs 46, 47, 48 from each other. The lugs 46, 47, 48 carry contacts 63, 64, 65 on their' underside and these cooperate each with its associated fixed 'contact"'66, 67, 68.

The switch is caused to ip to the open circuit condition by downward pressure applied to the internal edge of the arcuate projections 49, 50, 51, as shown diagrammatically in FIGURE 8 by the downwardly directed arrow. This may be done by a circular rod 69 co-axial with the stressed members having three collars 70, 71, 72, the underside of each collar normally resting on, or nearly resting on, its associated arcuate projection 49, 50, 51. Pressure on a knob 73, which may be screwed into the top of the rod 69 through an opening 74 in the cover 75, causes each collar 70, 71, 72 to apply pressure to its associated arcuate projection, and this causes each stressed member or blade 4t), 41, 42 to flip over to the opencircuit position. The operating rod 69 may be designed to apply pressure substantially simultaneously to all three arcuate projections, in which case kall three blades open substantially simultaneously, or to apply pressure to the projections in a desired order, in which case the three poles may be caused to open in a desired order.

While in the circular form of switch shown, each stressed member is secured by a lug, and the contact is carried by another lug, where a single pole switch is concerned the stressed member may be a simple annular ring secured at one end of a diameter and stressed at the other end of the diameter where the contact is carried. The stressed member may then be supported at points on its outer circumference at points approximately defined by a tangent to the inner circle, the tangent being at right angles to the diameter containing the securing point and the contact. A single pole switch of this type is miniaturized form can be built with an overall size of l0 mm. x 8 mm. x 3 mm. The diameter of the stressed member in this case is about 5.5 mm.

FIGURES 9 and l0 show a temperature dependent switch incorporating a microswitch in accordance with this invention and connected so as to be useful as an automobile flasher switch. The switch is dependent upon the temperature of an element in the switch, and in the form shown it is dependent upon the temperature of a stretched wire whose temperature is varied by an electric current passing through it. A circular insulating base 76 is provided as is common is such switches. An L-shaped main or support member 77 is secured to the base by means of its short arm- 78 and is channel shaped for rigidity. The long arm 79 of the main member lis apertured at 80 near its far end and also at 81 near the junction of the long arm with the short arm. The upper aperture has two projections 82, 83 into the channel on a line parallel to the end of the long arm for a purpose to be explained.

V The contact blade S4 of the microswitch, which is similar to that used in the switch of FIGURES 1 to 4, is secured to the top of the long arm of the main member, inside the channel, as -by screwing, as shown by nut and screw 85, or preferably rivetting or welding. The lower end of the contact blade 84 carries a contact 86 which extends into the lower aperture 81 in the long arm and co-operates with a fixed contact 87 secured to a bracket 88 which in turn is secured to the insulating base 76.

The contact blade 84 at points about on a level with the apex of the cutout 89 seats on the projections 82, 83 into the channel of the upper aperture in the support member. Pressure on the blade, between the transverse slot 90 and the apex of the cutout 89, directed toward the support member 77 will cause the free end of the blade to snap away from the main member, and so break the connection between the fixed and moving contacts 86, 87. This pressure is provided by a temperature dependent member.

The temperature dependent member includes a metal bow 91 having two arms 92, 93 bent to make an included angle slightly less than 90, one arm 93 being much shorter than the other. A nickel-iron alloy wire 94, such as those sold under the registered trademarks Nichrome and Brightray, is stretched between the ends of the bow,

hole or enlarged end of a slot 97 in the underside of the said short arm 93. The glass bead then serves to insulate one end of the wire from the bow, and this end is secured to one terminal 98 of the flasher. The bow is secured in the main or support member by means of a pin 99 passing through holes 100 in the flanges of the main member near the bend of the L and passing over the pivot formed by the junction of the arms of the bow. Other methods of securing such as welding may be' used. Essentially the short arm 93 of the bow is a substantially rigid member which is secured in position relative to the base 76 and support member 77 but to allow for initial adjustment a screw 101 is screwed into the base of the L-shaped support member with its head bearing against the underside of the short arm 92 of the boW. To allow the screw to be adjusted an opening 102 is provided in the said short arm of the bow, of lesser diameter than the head of the screw, through which the head of the grubscrew can be reached. The long arm of the'bow has a lug or outward protrusion 103 near its end which bears against the contact blade 84 of the microswit'ch between the transverse slot 90 and the apex of the cut-out 89. The initial pressure on the contact blade is adjusted by means of the screw 101.

Assume that current is flowing in the flasher circuit. It will flow 'from one terminal 98 of the unit to and through the wire 94, through the bow to the contact blade 84, and through the contacts 86, 87 to the other terminal of the fiasher. The current causes the wire to heat and expand, allowing the bow to unbend slightly, increasing the pressure on the contact blade 84, until finally the contact blade snaps over to open the current. The contacts then remain open until the wire cools sufiiciently to enable the contacts to close. The cycle is then repeated. To counteract ambient temperature effects the bow is made of Phosphor bronze which has a temperature coefficient of expansion similar to that of the wire. A suitable wire for a 12 volt flasher unit may have a diameter of .011 inch, and a length of 11A: inches.

Switches known as infinitely variable switches are used, among other things, to control the temperature of ovens and hot plates. They operate on the principle of switching the current on and off cyclically, the ratio of the on to the oft period being adjustable by means of a control knob. It is also necessary to provide an off position and a full-on position. The switch described above for use in a flasher unit may be readily modified to provide the infinitely variable switch shown in FIGURES 1l and l2.

In the infinitely variable switch the long arm of the support member is disposed horizontally with the short arm extending vertically upwards. The short arm of the support member is longer than in the flasher switch because, whereas in the flasher unit this arm had only to equal the length of the short arm ofthe bow, in the present application it also provides a bearing 104 above the bow for a control shaft 105. A further bearing 106 is provided at the other end of the switch. The control shaft carries a `face cam 107 adjacent the arm 78 of the support member with the cam face 108 against the side of the short arm 93 of the bow which faces the support member. The setting of the cam by the control shaft enables the pressure exerted by the temperature dependent member, the wire 94, upon the control blade 84 to be varied, thus varying the amount of expansion of the wire which is required before the switch contacts open. Accordingly means have been provided to vary the on-ofic ratio of the switch. The cam face is such that in one position of the control shaft the pressure exerted on the -contact blade at room temperature is more than sufficient to open the contacts, thus providing an off position. To ensure positive opening of the contacts in the off position even if the contacts should stick an apertured member 109 is provided which is slidable in the channel of the shortvv arm 78 of the support member, and which has a lug 110 at its lower end which engages under the end of the contact blade. In the off position a nib (not visible in the drawings) on the cam engages under a lug 111 at the top o-f the apertured member raising it and thus the contact blade to openthe switch. As the control shaft is rotated more and more from the off position the pressure of the bow onthe contact blade is decreased until finally the cam face 108 is well clear of the bow, giving a full-on position.

If the cam is of metal it should be insulated from the control shaft. Initial adjustment of the switch` can be provided in various ways. For example a hardened grub screw may be provided in the toe of the short arm of the bow which bears against the cam face. In a switch for a 1 kilowatt element the nickel-iron alloy wire may have a diameter of about 0.020 inch and a length of about 1% inches.

Temperature dependent switches in accordance with the invention have the advantage that the maximum stress occurs when the temperature dependent element is cold, that is, when the switch is being assembled, and that this maximum stress is known and preset. In contrast in the usual temperature dependent switches the stresses increase as the temperaturerises and may exceed allowable values. Furthermore the insulation requirements are low, the glass bead not being required to provide for more than about 4 volts.

A parallel type infinitely variable switch can be provided by winding an insulated heater winding over the Wire, the heater winding being connected in series with the contacts across the power source. In the known parallel type switches using bi-metallic strips -as the temperature dependent element the heater windings are expensive because they require special winding machines to allow for the extreme Variations in wire speed as the flat winding is being wound. The heater windings of the present invention are cylindrical and appreciably cheaper to Wind.

Ambient temperature compensation can be obtained to a large degree by making the bow and wire of metals having similar coefficients of expansion. Where the Wire Vis not heated electrically and the whole switch is exposed to temperature variations the bow and wire are made of metals having dissimilar temperature coefficients of expansion.

The glass bead can be replaced by a welded fermle and a small mica disc.

In some cases it is desirable to manually reset a thermal device. This can be done with switches in accordance with the invention by a slight variation in the stressing of the stressed member whereby it can be made nonreturning other than by manual means.

What I claim is:

1. A quick acting make-and-break multi-pole microswitch/comprising a base, a plurality of stressed exible annuli of strip metal, each annulus having a first externally projecting lug at one end of a diameter and a second externally projecting lug at the other end of the diameter,

means securing each annulus to the base by its first lug is bowed in the same direction, an internal projection on each annulus, and means applying pressure to each of the provided in various ways. For example a hardened grub internal projections so as to cause the centre of stress to pass from one side of each annulus to the other.

2. A quick acting make-and-break multi-pole microswitch comprising a base, a plurality of stressed flexible annuli of strip metal, each annulus having Ia first externally projecting lng at one end of a diameter and a second externally projecting lug at the other end of the diameter, means securing each annulus to the base by its rst lug so that the annuli are stacked one above the other and spaced from each other with the lugs displaced angularly with respect to each other, a contact on each said second lug, `fixed contacts on the base beneath the contact on each annulus, a bending of the metal of each annulus out of the plane of the annulus to thereby effectively shorten the circumference of the annulus whereby each annulus is bowed in the same direction, an internal projection on each of the annuli an actuating rod within said annuli and coaxial therewith, and collars on the actuating rod each of which engages with said internal projections a respective one of the annuli whereby pressure can be applied to the annuli.

3. A quick make-and-break rnicroswitch comprising a base, a stressed exible metal annulus secured to the base at one end of a diameter, -a contact on the annulus at the other end of the said diameter, a permanent bending of the metal at the contact end of the diameter out of the plane of the annulus to thereby effectively shorten the circumference of the annulus whereby the annulus takes up a bowed formation, supports for the annulus at spaced points adjacent to the inner circle of the annulus at the secured end of the diameter, a nib projecting internally from the annulus between the said supports, and means applying pressure to the annulus.

4. A quick make-and-break rnicroswitch comprising -a base,a stressed exible metal annulus, a rst lug at one end of a diameter of the annulus, securing means by which the rst lug is secured to the base, a second lug at the other end of the diameter of the annulus, a cont-act on the second lug, a permanent bending of the' metal of the annulus at the second lug to thereby effectively shorten the circumference of the annulus whereby the annulus takes up a bowed formation, supports for the annulus at spaced points adjacent to the inner circle of the annulus at the said rst lug end of the diameter, a projection from the inner circle of the annulus between the said supports, means applying pressure to the said projection so as to cause the centre of stress to pass from one side of the annulus to the other, and a slot in the annulus between the said last-mentioned projection and the said first lug.

References Cited by the Examiner UNITED STATES PATENTS 2,301,129 11/1942 Lehmann 200-120 X 2,324,798 7/1943 Nordberg 200-67 2,363,280 11/1944 Arnold 200-113 X 2,513,053 6/ 1950 Roswell 200-67 2,624,819 1/1953 Spina et al. 200--122 X 2,776,347 1/1957 Allen 200,-67 2,971,069 2/1961 Good 200-67 3,172,970 3/1965 Abele et al. 200-138 X FOREIGN PATENTS 661,970 4/1963 Canada. 716,096 9/1954 Great Britain 200-133 BERNARD A. GILHEANY, Primary Examiner.

B. DOBECK, Examiner.

L. A. WRIGHT, T. MACBLAIN, Assistant Examiners. 

3. A QUICK MAKE-AND-BREAK MICROSWITCH COMPRISING A BASE, A STRESSED FLEXIBLE METAL ANNULUS SECURED TO THE BASE AT ONE END OF A DIAMETER, A CONTACT ON THE ANNULUS AT THE OTHER END OF THE SAID DIAMETER, A PERMANENT BENDING OF THE METAL AT THE CONTACT END OF THE DIAMETER OUT OF THE PLANE OF THE ANNULUS TO THEREBY EFFECTIVELY SHORTEN THE CIRCUMFERENCE OF THE ANNULUS WHEREBY THE ANNULUS TAKES UP A BOWED FORMATION, SUPPORTS FOR THE ANNULUS AT SPACED POINTS ADJACENT TO THE INNER CIRCLE OF THE ANNULUS AT THE 